I'm always puzzled when so-called forward-thinking individuals claim the Catholic Church's teaching on sexuality is outmoded and obsolete. That claim, of course, implies that at one time Catholic moral teaching was relevant and appropriate and that, as time has passed and as sexual mores have loosened and gender roles grown nontraditional, the Church's teachings no longer apply.
The most appropriate reaction to such piffle is to box the speaker on the ears. But if one prefers not to touch the heretic, kindly lead him to the nearest history textbook, and open it up to the chapter on PAGAN ROME: SEXUAL MORES.
Remind him that pagan Rome was the birthplace of Christianity, and that the Church's battles against 21st-century American sexual ideals is a walk in the park compared to its struggles in 1st-century Rome. Remind him that modern American culture--as degraded as it may be--doesn't hold a candle to the decadence of Rome (or of Greece, for that matter). Remind him that Christian bishops had no easier a time teaching their flock to remain chaste then than they do today--but teach it they did, faithfully, in the face of ridicule, unpopularity, and even martyrdom. And the early Church surely had her dissident few who thought they could make the faith more palatable to secular Rome if only the Church would relax a bit on her sexual teachings, who argued that Catholic morality couldn't compete with the rampant adultery, concubinage, homosexuality, and pedophilia. Remind him, however, that, not only did it compete, it conquered, and once-pagan Rome became the seat of the Holy See, the head of the universal church, and the leader of the largest religious group in the world.
That should shut him up.